It is known to provide yarns or fabrics with multicomponent fibers of two dissimilar acrylonitrile polymeric components eccentrically disposed toward each other in distinct zones extending throughout the length of the fiber with adjoining surfaces in intimate adhering contact. Such fibers are disclosed in U.S. Pat. No. 3,330,896, to Fujita et al. The components in these fibers have different thermal shrinkages and result upon heat treatment in fibers having a three dimensional crimp.
It is further known to provide bicomponent foams wherein two different foams with differing physical characteristics are integrally joined in a mold during formation. Such bicomponent foams generally do not have any fire resistant characteristics and are used for their resiliency and compressibility.
To provide the prior art multicomponent polymeric materials with fire resistance would normally require the addition of a further component or additive which prevents ignition.
Current methods for providing fire resistance to polymeric materials require blending with a fire resistant organic material as a major component in a mixture. Fiber blends with high performance fibers such as, for example, KEVLAR (a trademark of E. I. du Pont de Nemours & Co. for p-aramid) with a limited oxygen index (LOI) of 29 according to test method ASTM D2863-77, polybenzimidazole (LOI 40), PANOX (a trademark of R. K. Textiles Composite Fibers, Ltd. for oxidized polyacrylonitrile) (LOI 55) are commonly utilized. Examples of these include fire resistant blends of KEVLAR-cotton or KEVLAR-polyester wherein the KEVLAR must be present at levels well above 60 weight percent.
Other methods include adding various chemical additives or coatings such as phosphorous or halogen containing compounds. However, the fire resistant performance is minimal, undependable and subject to neutralization.
Various methods are known to reduce the flammability of polymeric foams. Commonly, additives such as aluminum trihydrate or phosphorus-containing compounds are incorporated into the foam as a flame retardant. Alternatively, halogenated polyols, bromine containing compounds or modacrylics are used in connection with polyurethanes to increase the flame resistance of the foam. None of these additives have proved entirely satisfactory.
It is known that the incorporation of trimerized polyisocyanates (i.e. isocyanaurates) into a polyurethane foam improves its burn characteristics. For example, trimerized toluenediisocyanate has been used to prepare flexible foams. Although these foams do exhibit good foam forming characteristics, they also have poor physical properties, particularly, poor compression sets and partial cell collapse.
With particular reference to the physical and mechanical properties of foams, they are extremely useful for a wide variety of application, including insulation, upholstery and bedding. However, many foams, for example polyurethane foams, are inherently flammable and lead to melting and the spread of burning polymer particles or droplets. In the case of many "conventional" foams, such characteristics lead to a sustained combustion due to progressive smoldering even after the actual flames have been extinguished.
It is known that cellular materials manufactured from flammable polymers are more flammable than solid polymeric materials because the insulating effect of the cellular structure allows for a rapid build-up of heat at the heating surface with a consequential high rate of pyrolysis.
U.S. patent application Ser. No. 480,416, filed Feb. 15, 1990 of Mc Cullough et al, which is herein incorporated by reference, discloses fire resistant monocomponent fibers, films and foams. There is further disclosed the precursor materials which can be used in the present invention.
U.S. Pat. No. 3,639,953, to Kimura et al discloses a bicomponent fiber wherein pitch and a polymeric material are concurrently spun and bonded together longitudinally, and then both components are oxidized and carbonized.
U.S. Pat. No. 3,811,997, to E. L. Yaun discloses smoke and flame resistant structural articles for use in aircraft. The articles can be of a laminate or a honeycomb construction. The articles are provided with a thin film of polyimide or polyamide to retard combustion of the underlying laminate and reduce smoke effusion from any burning that does occur.
U.S. Pat. No. 4,832,881, to Arnold, Jr. et al discloses a low density microcellular carbon foam for use as catalysts, adsorbents and electrodes. These foams, which are prepared from oxidized polyacrylonitrile, have a density greater than 1.39 g/cc.
U.S. Pat. No. 4,255,483, to N. R. Byrd et al discloses an acoustic firewall for use in environments such as an aircraft engine nacelle. The firewall includes a graphite fiber or glass cloth embedded in a silica-containing polyimide resin. The presence of the silica is described as being necessary to provide the polyimide resin and the firewall with the desired stability in the presence of a fire and with low thermal conductivity.
U.S. Pat. No. 4,837,076, to Mc Cullough et al relates to the preparation of nonlinear carbonaceous fibers. U.S. Pat. No. 4,879,168, to Mc Cullough et al relates to thermal insulating and sound absorbing structures employing nonlinear carbonaceous fibers and to classes of such fibers having different electroconductivity which can be used in the present invention. Each of these patents are incorporated herein by reference.
Representative of the state of the art relating to carbonaceous foams is U.S. Pat. No. 4,832,870, to Sylwester et al which discloses a carbon foam that is filled with polymeric resin and which contains reinforcing carbon or glass fibers.
It is understood that the term "fire resistant" as used herein relates to any one of the characteristics of flame arresting, flame retarding, fire shielding and fire barrier.
An article is considered to be flame retarding to the extent that once an igniting flame has ceased to contact unburned parts of the textile structure, the article has the inherent ability to resist further propagation of the flame along its unburned portion, thereby stopping the internal burning process. Recognized tests to determine whether a textile article is flame retarding, inter alia, are the American Association of Textile Chemists and Colorists Test Method 34-1966 and the National Bureau of Standards Test described in DOC FF 3-71.
An article is considered to be "flame arresting," if it has the ability to block flames from contact with an unburned part of a flammable substance for at least five minutes.
An article is considered to be "fire shielding," if it is capable of deflecting flames and the radiation therefrom in a similar manner as aluminum coated protective garments which are known in the art.
Fire barriers have the capability of being non-flammable, flame retarding and providing thermal insulation characteristics.
The term "carbonaceous" used herein relates to polymeric substances whose carbon content have been irreversibly increased as a result of a chemical reaction such as a heat treatment, as disclosed in U.S. Pat. No. 4,837,076.
The term "non-graphitic" as used herein relates to those carbonaceous materials, which are substantially free of oriented carbon or graphite microcrystals of the three dimensional order that typically have an elemental carbon content of less than 98% and as defined in U.S. Pat. No. 4,005,183, which is herein incorporated by reference.
The term "flash heat treatment" as utilized herein refers to a heat treatment of the polymeric material for a short period of time at elevated temperatures by control of either the term of stay polymeric material in a heating environment or the state of control of the heat source.